Influence of changes in pH on the mechanical activity of cardiac muscle.

In a comprehensive experimental study, the influence of changes in extraand intracellular pH on the mechanical and electrical activity of frog heart ventricle preparations has been investigated. The twitch tension and potassium contracture tension were decreased in acid solutions, provided that the concentration of calcium or the frequency of stimulation was low. In solutions with a high calcium concentration, prolonged exposure to acid leads to an increase of the potassium contractures. The electrical activity, measured by intracellular microelectrodes, is abolished in acid solutions if the change of solution in the extracellular space is enforced by perpendicular jet superfusion; with slow perfusion it is well maintained except when [Ca] is high. The lowering of intracellular pH by applying a solution saturated with 80% CO2 while keeping the extracellular pH constant causes a rapid drop in twitch tension followed by partial recovery. The relaxation phase of single twitches is prolonged and potassium contractures are markedly increased after the high CO2 has acted for several minutes. When both intraand extracellular pH are decreased, both twitches and potassium contractures are markedly decreased. The electrical activity is maintained. Some of the effects of variations in pH are discussed in terms of changes in the processes of mechanical activation and inactivation. ADDITIONAL